Existing aeronautical data link services based on VHF ground stations, which are installed across landmasses to provide line-of-sight air-to-ground data link communications, are relatively expensive for airspace users. This is in part due to capital equipment required to install the ground stations as well as on going maintenance costs. In particular, current domestic aeronautical data links (ACARS) use an expensive, in terms of both capital and maintenance, ground station network where the ground stations are spaced approximately every 150 miles, where 150 miles is the approximate radio range of VHF communications from an aircraft. This results in hundreds of ground stations, used only for aeronautical data link, in high density domestic airspaces in the US, Europe and other areas around the world. These ACARS networks work in a star configuration where ground stations are connected to a central processor which serves as the master router. The central processor knows the ground station used for a downlink from an aircraft and uses that same ground station for an uplink to the aircraft. If the aircraft does not respond to an uplink, the central processor sends the message out via adjacent ground stations until it finds the aircraft.
Air-to-air networking provides one possible solution which does not rely on capital intensive ground stations. In an air-to-air network, aircraft form mobile nodes capable of relaying messages from one aircraft to another aircraft or to a ground station at the intended destination which is beyond the communication range of the originating aircraft. Air-to-air networks, where the message is relayed entirely via the air-to-air network from the source to the destination, however, have a disadvantage when a message needs to be relayed over a long distance because they consume more radio frequency spectrum than direct air-to-ground communications.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a cost effective method for aeronautical communications.